This invention relates generally to golf ball property measurement. Still more particularly, this invention relates to an apparatus and method for testing golf ball properties including coefficient of restitution and contact time.
There is significant prior art for determining the hardness of a golf ball, including Atti compression, Reihle compression, the compression based on deformation of a ball under a 100 kg load and the compression of a ball under a 30 kg load. However, the prior art for identifying the stiffness of golf balls normally does not take into account the influence of deformation rate on xe2x80x9cstiffness.xe2x80x9d That is, golf ball, or core, stiffness is typically measured by means of a low rate compression test. These tests are performed by applying a fixed load or a fixed deflection to the ball or core and by measuring displacement or load, respectively. The rate of load application in these tests range from 0.1 to 60 seconds, for the various industry standard tests (e.g., Atti, Reihle). The time for deformation of a golf ball on a typical driver during an ordinary impact is on the order of 0.0005 seconds, or, on the order of 2000 times faster than industry standard compression tests. It is well known that the polymeric materials used in golf balls have rate dependent stiffness. At high rates the stiffness may be as much as 10 times greater than stiffness measured at low rate. Therefore, prior art compression or stiffness measures usually do not reflect the stiffness of a ball in actual use conditions.
U.S. Pat. No. 3,509,736 to Saari discloses an apparatus for measuring the coefficient of restitution of spherical bodies. The apparatus applies a fixed velocity to the spherical body and computes the coefficient of restitution. The ball is held on a tee in an unrestrained manner. The ball is struck by a device causing the ball to move horizontally intercepting a beam from a photocell and continuing through a flight tube until it passes a light screen and a deflecting surface (such as a curtain). The device then uses the measurements to calculate the coefficient of restitution.
U.S. Pat. No. 5,245,862 to Zeiss discloses a portable testing device and method for determining the coefficient of restitution of a rebounding object. The method compares the bounce periods of successive bounces of the object. A ball is dropped on a reaction plate, the ball bounces at least three times on the reaction plate. Each impact is detected and the time of the bounce interval between successive bounces is measured. The coefficient of restitution is then calculated by comparing the bounce intervals as a ratio of the time between impacts of the second bounce interval to the first bounce interval. The device includes a reaction plate with a large mass in comparison with the ball, a transducer for registering the impact of the ball. A display is also included having a timer and a clock for measuring the bounce intervals and calculating the coefficient of restitution.
U.S. Pat. No. 5,672,809 to Brandt discloses a system for determining the coefficient of restitution between first and second pieces of sporting equipment. The system mounts a first piece of sporting equipment such as a bat, golf club or tennis racket. The first piece is held at a certain position and impacted by a second piece of sporting equipment, such as a baseball, golf ball or tennis ball. The device measures the velocity of the second piece of sporting equipment and the rebound velocity of the first piece of sporting equipment after impact. The coefficient of restitution is then determined using the measured information.
Nevertheless, it is desirable to have an apparatus to quantify the dynamic stiffness by means of contact duration while simultaneously acquiring coefficient of restitution.
The present invention is directed to an apparatus for measuring the physical properties of an object, the apparatus including: a propelling device that fires the object; a striking surface facing the propelling device; a sensing unit located between the striking surface and the propelling device, wherein the sensing unit has a measuring field covering a space between the propelling device and the striking surface, and wherein the sensing unit is capable of measuring the time it takes for the object to travel a distance in the measuring field of the sensing unit; and a computing unit that calculates the impact duration between the object and the striking surface and the Coefficient of Restitution of the object, wherein the computing unit is in communication with the sensing unit. In one embodiment, the propelling device is an air cannon. In another embodiment, the mass of the striking surface is at least about 50 times greater than the mass of the object. The object preferably includes a golf ball component.
In one embodiment, the sensing unit further includes a first sensing device at a first position and a second sensing device at a second position, the second sensing device being spaced apart from the first sensing device. Preferably, one of the sensing devices is a light gate. In one embodiment, the light gate is a solid state ballistics screen. In another embodiment, one of the sensing devices includes a plurality of sensors.
In one embodiment, the first sensing device has a sensing field covering a first predetermined plane and the second sensing device has a sensing field covering a second predetermined plane, the second predetermined plane being parallel and at a predetermined distance Y from the first predetermined plane. In one embodiment, the predetermined distance Y is about 12 inches or greater, and in another, the predetermined distance Y is about 4 feet or greater.
The apparatus can further include a third sensing device located near the striking surface for measuring the time in which the object is in contact with the striking surface. In one embodiment, the third sensing device includes a plurality of sensors. In another embodiment, the third sensing device has a sensing field covering a predetermined plane, wherein the the predetermined plane is preferably parallel and at a predetermined distance A from the striking surface. In a preferred embodiment, the predetermined distance A is about 1 inch or less, and more preferably about 0.25 inches or less.
In one embodiment, at least one of the sensors is a fiber optic sensor. Preferably, the fiber optic sensor includes a computer interface card and a fiber optic receiver electrically connected to the input of the computer interface card for counting the time in which the object is in contact with the striking surface.
The propelling device can fire the object in a horizontal or vertical direction.
The present invention is also directed to an apparatus for the simultaneous measurement of contact time and Coefficient of Restitution of an object, the apparatus including: a propelling device that fires the object; a striking surface facing the propelling device; at least one sensing device at a first position having a first sensing plane; a timing device triggered by the at least one sensing device; at least one camera triggered by the at least one sensing device to acquire at least a first and second pair of images before and after the object contacts the striking surface, respectively; and a computing unit that calculates the Coefficient of Restitution of the object and the contact time between the object and the striking surface. Each pair of images preferably includes a first and second image taken at two discrete time intervals.
In one embodiment, the apparatus further includes a second sensing device at a second position having a second sensing plane, wherein the second sensing device is parallel and at a predetermined distance A from the striking surface. The second sensing device preferably includes at least one fiber optic sensor. In one embodiment, the at least one fiber optic sensor includes a computer interface card and a fiber optic receiver electrically connected to the input of the computer interface card for counting the time in which the object stays past the second sensing device.
In another embodiment, the apparatus further includes a second camera to acquire at least a third and fourth pair of images before and after the object contacts the striking surface, respectively.
The present invention is also directed to a method of measuring Coefficient of Restitution and contact time of an object including the steps of: directing an object towards a striking surface; measuring a first velocity of the object before it contacts the striking surface; measuring impact duration of the object with the striking surface; measuring a second velocity of the object after it rebounds from the striking surface; and calculating the Coefficient of Restitution.
In one embodiment, the method further includes the step of providing at least one sensing unit having a measuring field covering at least a portion of space between an initial position of the object and the striking surface, wherein the at least one sensing unit measures the time required for the object to travel a distance in the measuring field of the sensing unit.
In another embodiment, the method further includes the step of providing a computing unit in communication with the at least one sensing unit that calculates the Coefficient of Restitution of the object and impact duration between the object and the striking surface.
The mass of the striking surface is preferably at least about 50 times greater than the mass of the object.
In one embodiment, the step of releasing the object is done horizontally, and in another embodiment, the step of releasing the object is done vertically.
In one embodiment, the method further includes the step of providing at least one camera to acquire at least a first and second pair of images before and after the object contacts the striking surface, respectively.
In another embodiment, the method further includes the step of providing a second sensing unit having a second measuring field covering a space between the at least one sensing unit and the striking surface, wherein the second sensing unit is parallel and at a predetermined distance from the striking surface.
In yet another embodiment, the method further includes the step of providing a second camera to acquire at least a third and fourth pair of images before and after the object contacts the striking surface, respectively.